This module can be configured to provide several items of SSL information
as additional environment variables to the SSI and CGI namespace. This
information is not provided by default for performance reasons. (See
SSLOptions StdEnvVars, below.) The generated variables
are listed in the table below. For backward compatibility the information can
be made available under different names, too. Look in the Compatibility chapter for details on the
compatibility variables.

x509 specifies a component of an X.509 DN; one of
C,ST,L,O,OU,CN,T,I,G,S,D,UID,Email. In Apache 2.1 and
later, x509 may also include a numeric _n
suffix. If the DN in question contains multiple attributes of the
same name, this suffix is used as an index to select a particular
attribute. For example, where the server certificate subject DN
included two OU fields, SSL_SERVER_S_DN_OU_0 and
SSL_SERVER_S_DN_OU_1 could be used to reference each.

When mod_ssl is built into Apache or at least
loaded (under DSO situation) additional functions exist for the Custom Log Format of
mod_log_config. First there is an
additional ``%{varname}x''
eXtension format function which can be used to expand any variables
provided by any module, especially those provided by mod_ssl which can
you find in the above table.

For backward compatibility there is additionally a special
``%{name}c'' cryptography format function
provided. Information about this function is provided in the Compatibility chapter.

This directive sets the all-in-one file where you can assemble the
Certificates of Certification Authorities (CA) whose clients you deal
with. These are used for Client Authentication. Such a file is simply the
concatenation of the various PEM-encoded Certificate files, in order of
preference. This can be used alternatively and/or additionally to
SSLCACertificatePath.

This directive sets the directory where you keep the Certificates of
Certification Authorities (CAs) whose clients you deal with. These are used to
verify the client certificate on Client Authentication.

The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you can't just place the Certificate files
there: you also have to create symbolic links named
hash-value.N. And you should always make sure this directory
contains the appropriate symbolic links.

When a client certificate is requested by mod_ssl, a list of
acceptable Certificate Authority names is sent to the client
in the SSL handshake. These CA names can be used by the client to
select an appropriate client certificate out of those it has
available.

In some circumstances, it is useful to be able to send a set of
acceptable CA names which differs from the actual CAs used to verify
the client certificate - for example, if the client certificates are
signed by intermediate CAs. In such cases, SSLCADNRequestPath and/or SSLCADNRequestFile can be used; the
acceptable CA names are then taken from the complete set of
certificates in the directory and/or file specified by this pair of
directives.

SSLCADNRequestFile must
specify an all-in-one file containing a concatenation of
PEM-encoded CA certificates.

This optional directive can be used to specify the set of
acceptable CA names which will be sent to the client when a
client certificate is requested. See the SSLCADNRequestFile directive for more
details.

The files in this directory have to be PEM-encoded and are accessed
through hash filenames. So usually you can't just place the
Certificate files there: you also have to create symbolic links named
hash-value.N. And you should always make sure
this directory contains the appropriate symbolic links.

This directive sets the all-in-one file where you can
assemble the Certificate Revocation Lists (CRL) of Certification
Authorities (CA) whose clients you deal with. These are used
for Client Authentication. Such a file is simply the concatenation of
the various PEM-encoded CRL files, in order of preference. This can be
used alternatively and/or additionally to SSLCARevocationPath.

This directive sets the directory where you keep the Certificate Revocation
Lists (CRL) of Certification Authorities (CAs) whose clients you deal with.
These are used to revoke the client certificate on Client Authentication.

The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you have not only to place the CRL files there.
Additionally you have to create symbolic links named
hash-value.rN. And you should always make sure this directory
contains the appropriate symbolic links.

This directive sets the optional all-in-one file where you can
assemble the certificates of Certification Authorities (CA) which form the
certificate chain of the server certificate. This starts with the issuing CA
certificate of the server certificate and can range up to the root CA
certificate. Such a file is simply the concatenation of the various
PEM-encoded CA Certificate files, usually in certificate chain order.

This should be used alternatively and/or additionally to SSLCACertificatePath for explicitly
constructing the server certificate chain which is sent to the browser
in addition to the server certificate. It is especially useful to
avoid conflicts with CA certificates when using client
authentication. Because although placing a CA certificate of the
server certificate chain into SSLCACertificatePath has the same effect
for the certificate chain construction, it has the side-effect that
client certificates issued by this same CA certificate are also
accepted on client authentication.

But be careful: Providing the certificate chain works only if you are using a
single RSA or DSA based server certificate. If you are
using a coupled RSA+DSA certificate pair, this will work only if actually both
certificates use the same certificate chain. Else the browsers will be
confused in this situation.

This directive points to a file with certificate data in PEM format.
At a minimum, the file must include an end-entity (leaf) certificate.
The directive can be used up to three times (referencing different filenames)
when an RSA, a DSA, and an ECC based server certificate is used in parallel.

Custom DH parameters and an EC curve name for ephemeral keys,
can be added to end of the first file configured using
SSLCertificateFile.
This is supported in version 2.2.30 or later.
Such parameters can be generated using the commands
openssl dhparam and openssl ecparam.
The parameters can be added as-is to the end of the first
certificate file. Only the first file can be used for custom
parameters, as they are applied independently of the authentication
algorithm type.

Finally the the end-entity certificate's private key can also be
added to the certificate file instead of using a separate
SSLCertificateKeyFile
directive. This practice is highly discouraged. If the private
key is encrypted, the pass phrase dialog is forced at startup time.

DH parameter interoperability with primes > 1024 bit

Beginning with version 2.2.30, mod_ssl makes use of
standardized DH parameters with prime lengths of 2048, 3072, 4096, 6144 and
8192 bits (from RFC 3526),
and hands them out to clients based on the length of the certificate's RSA/DSA
key.
With Java-based clients in particular (Java 7 or earlier), this may lead
to handshake failures - see this
FAQ answer for working around
such issues.

This directive points to the PEM-encoded private key file for the
server. If the contained private key is encrypted, the pass phrase
dialog is forced at startup time.

The directive can be used up to three times (referencing different filenames)
when an RSA, a DSA, and an ECC based private key is used in parallel. For each
SSLCertificateKeyFile
directive, there must be a matching SSLCertificateFile
directive.

The private key may also be combined with the certificate in the file given by
SSLCertificateFile, but this practice
is highly discouraged.

This complex directive uses a colon-separated cipher-spec string
consisting of OpenSSL cipher specifications to configure the Cipher Suite the
client is permitted to negotiate in the SSL handshake phase. Notice that this
directive can be used both in per-server and per-directory context. In
per-server context it applies to the standard SSL handshake when a connection
is established. In per-directory context it forces a SSL renegotiation with the
reconfigured Cipher Suite after the HTTP request was read but before the HTTP
response is sent.

An SSL cipher specification in cipher-spec is composed of 4 major
attributes plus a few extra minor ones:

Key Exchange Algorithm:
RSA or Diffie-Hellman variants.

Authentication Algorithm:
RSA, Diffie-Hellman, DSS or none.

Cipher/Encryption Algorithm:
DES, Triple-DES, RC4, RC2, IDEA or none.

MAC Digest Algorithm:
MD5, SHA or SHA1.

An SSL cipher can also be an export cipher and is either a SSLv2 or SSLv3/TLSv1
cipher (here TLSv1 is equivalent to SSLv3). To specify which ciphers to use,
one can either specify all the Ciphers, one at a time, or use aliases to
specify the preference and order for the ciphers (see Table
1).

Now where this becomes interesting is that these can be put together
to specify the order and ciphers you wish to use. To speed this up
there are also aliases (SSLv2, SSLv3, TLSv1, EXP, LOW, MEDIUM,
HIGH) for certain groups of ciphers. These tags can be joined
together with prefixes to form the cipher-spec. Available
prefixes are:

none: add cipher to list

+: move matching ciphers to the current location in list

-: remove cipher from list (can be added later again)

!: kill cipher from list completely (can not be added later again)

aNULL, eNULL and EXP
ciphers are always disabled

Beginning with version 2.2.30, null and export-grade
ciphers are always disabled, as mod_ssl unconditionally prepends any supplied
cipher suite string with !aNULL:!eNULL:!EXP: at initialization.

A simpler way to look at all of this is to use the ``openssl ciphers
-v'' command which provides a nice way to successively create the
correct cipher-spec string. The default cipher-spec string
is ``ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP'' which
means the following: first, remove from consideration any ciphers that do not
authenticate, i.e. for SSL only the Anonymous Diffie-Hellman ciphers. Next,
use ciphers using RC4 and RSA. Next include the high, medium and then the low
security ciphers. Finally pull all SSLv2 and export ciphers to the
end of the list.

Available in Apache 2.1 and later, if using -engine flavor of OpenSSL
0.9.6, or OpenSSL 0.9.7 or later

This directive enables use of a cryptographic hardware accelerator
board to offload some of the SSL processing overhead. This directive
can only be used if the SSL toolkit is built with "engine" support;
OpenSSL 0.9.7 and later releases have "engine" support by default, the
separate "-engine" releases of OpenSSL 0.9.6 must be used.

To discover which engine names are supported, run the command
"openssl engine".

This directive toggles the usage of the SSL/TLS Protocol Engine. This
should be used inside a <VirtualHost> section to enable SSL/TLS for a
that virtual host. By default the SSL/TLS Protocol Engine is
disabled for both the main server and all configured virtual hosts.

Example

<VirtualHost _default_:443>
SSLEngine on
...
</VirtualHost>

In Apache 2.1 and later, SSLEngine can be set to
optional. This enables support for
RFC 2817, Upgrading to TLS
Within HTTP/1.1. At this time no web browsers support RFC 2817.

This directive toggles the usage of the SSL library FIPS_mode flag.
It must be set in the global server context and cannot be configured
with conflicting settings (SSLFIPS on followed by SSLFIPS off or
similar). The mode applies to all SSL library operations.

If httpd was compiled against an SSL library which did not support
the FIPS_mode flag, SSLFIPS on will fail. Refer to the
FIPS 140-2 Security Policy document of the SSL provider library for
specific requirements to use mod_ssl in a FIPS 140-2 approved mode
of operation; note that mod_ssl itself is not validated, but may be
described as using FIPS 140-2 validated cryptographic module, when
all components are assembled and operated under the guidelines imposed
by the applicable Security Policy.

As originally specified, all versions of the SSL and TLS protocols
(up to and including TLS/1.2) were vulnerable to a Man-in-the-Middle
attack
(CVE-2009-3555)
during a renegotiation. This vulnerability allowed an attacker to
"prefix" a chosen plaintext to the HTTP request as seen by the web
server. A protocol extension was developed which fixed this
vulnerability if supported by both client and server.

If mod_ssl is linked against OpenSSL version 0.9.8m
or later, by default renegotiation is only supported with
clients supporting the new protocol extension. If this directive is
enabled, renegotiation will be allowed with old (unpatched) clients,
albeit insecurely.

Security warning

If this directive is enabled, SSL connections will be vulnerable to
the Man-in-the-Middle prefix attack as described
in CVE-2009-3555.

Example

SSLInsecureRenegotiation on

The SSL_SECURE_RENEG environment variable can be used
from an SSI or CGI script to determine whether secure renegotiation is
supported for a given SSL connection.

This configures the SSL engine's semaphore (aka. lock) which is used for mutual
exclusion of operations which have to be done in a synchronized way between the
pre-forked Apache server processes. This directive can only be used in the
global server context because it's only useful to have one global mutex.
This directive is designed to closely match the
AcceptMutex directive.

The following Mutex types are available:

none | no

This is the default where no Mutex is used at all. Use it at your own
risk. But because currently the Mutex is mainly used for synchronizing
write access to the SSL Session Cache you can live without it as long
as you accept a sometimes garbled Session Cache. So it's not recommended
to leave this the default. Instead configure a real Mutex.

posixsem

This is an elegant Mutex variant where a Posix Semaphore is used when possible.
It is only available when the underlying platform
and APR supports it.

sysvsem

This is a somewhat elegant Mutex variant where a SystemV IPC Semaphore is used when
possible. It is possible to "leak" SysV semaphores if processes crash before
the semaphore is removed. It is only available when the underlying platform
and APR supports it.

sem

This directive tells the SSL Module to pick the "best" semaphore implementation
available to it, choosing between Posix and SystemV IPC, in that order. It is only
available when the underlying platform and APR supports at least one of the 2.

pthread

This directive tells the SSL Module to use Posix thread mutexes. It is only available
if the underlying platform and APR supports it.

fcntl:/path/to/mutex

This is a portable Mutex variant where a physical (lock-)file and the fcntl()
function are used as the Mutex.
Always use a local disk filesystem for /path/to/mutex and never a file
residing on a NFS- or AFS-filesystem. It is only available when the underlying platform
and APR supports it. Note: Internally, the Process ID (PID) of the
Apache parent process is automatically appended to
/path/to/mutex to make it unique, so you don't have to worry
about conflicts yourself. Notice that this type of mutex is not available
under the Win32 environment. There you have to use the semaphore
mutex.

flock:/path/to/mutex

This is similar to the fcntl:/path/to/mutex method with the
exception that the flock() function is used to provide file
locking. It is only available when the underlying platform
and APR supports it.

file:/path/to/mutex

This directive tells the SSL Module to pick the "best" file locking implementation
available to it, choosing between fcntl and flock,
in that order. It is only available when the underlying platform and APR supports
at least one of the 2.

default | yes

This directive tells the SSL Module to pick the default locking implementation
as determined by the platform and APR.

This directive can be used to control various run-time options on a
per-directory basis. Normally, if multiple SSLOptions
could apply to a directory, then the most specific one is taken
completely; the options are not merged. However if all the
options on the SSLOptions directive are preceded by a
plus (+) or minus (-) symbol, the options
are merged. Any options preceded by a + are added to the
options currently in force, and any options preceded by a
- are removed from the options currently in force.

The available options are:

StdEnvVars

When this option is enabled, the standard set of SSL related CGI/SSI
environment variables are created. This per default is disabled for
performance reasons, because the information extraction step is a
rather expensive operation. So one usually enables this option for
CGI and SSI requests only.

ExportCertData

When this option is enabled, additional CGI/SSI environment variables are
created: SSL_SERVER_CERT, SSL_CLIENT_CERT and
SSL_CLIENT_CERT_CHAIN_n (with n = 0,1,2,..).
These contain the PEM-encoded X.509 Certificates of server and client for
the current HTTPS connection and can be used by CGI scripts for deeper
Certificate checking. Additionally all other certificates of the client
certificate chain are provided, too. This bloats up the environment a
little bit which is why you have to use this option to enable it on
demand.

FakeBasicAuth

When this option is enabled, the Subject Distinguished Name (DN) of the
Client X509 Certificate is translated into a HTTP Basic Authorization
username. This means that the standard Apache authentication methods can
be used for access control. The user name is just the Subject of the
Client's X509 Certificate (can be determined by running OpenSSL's
openssl x509 command: openssl x509 -noout -subject -in
certificate.crt). Note that no password is
obtained from the user. Every entry in the user file needs this password:
``xxj31ZMTZzkVA'', which is the DES-encrypted version of the
word `password''. Those who live under MD5-based encryption
(for instance under FreeBSD or BSD/OS, etc.) should use the following MD5
hash of the same word: ``$1$OXLyS...$Owx8s2/m9/gfkcRVXzgoE/''.

StrictRequire

This forces forbidden access when SSLRequireSSL or
SSLRequire successfully decided that access should be
forbidden. Usually the default is that in the case where a ``Satisfy
any'' directive is used, and other access restrictions are passed,
denial of access due to SSLRequireSSL or
SSLRequire is overridden (because that's how the Apache
Satisfy mechanism should work.) But for strict access restriction
you can use SSLRequireSSL and/or SSLRequire in
combination with an ``SSLOptions +StrictRequire''. Then an
additional ``Satisfy Any'' has no chance once mod_ssl has
decided to deny access.

OptRenegotiate

This enables optimized SSL connection renegotiation handling when SSL
directives are used in per-directory context. By default a strict
scheme is enabled where every per-directory reconfiguration of
SSL parameters causes a full SSL renegotiation handshake. When this
option is used mod_ssl tries to avoid unnecessary handshakes by doing more
granular (but still safe) parameter checks. Nevertheless these granular
checks sometimes maybe not what the user expects, so enable this on a
per-directory basis only, please.

When Apache starts up it has to read the various Certificate (see
SSLCertificateFile) and
Private Key (see SSLCertificateKeyFile) files of the
SSL-enabled virtual servers. Because for security reasons the Private
Key files are usually encrypted, mod_ssl needs to query the
administrator for a Pass Phrase in order to decrypt those files. This
query can be done in two ways which can be configured by
type:

builtin

This is the default where an interactive terminal dialog occurs at startup
time just before Apache detaches from the terminal. Here the administrator
has to manually enter the Pass Phrase for each encrypted Private Key file.
Because a lot of SSL-enabled virtual hosts can be configured, the
following reuse-scheme is used to minimize the dialog: When a Private Key
file is encrypted, all known Pass Phrases (at the beginning there are
none, of course) are tried. If one of those known Pass Phrases succeeds no
dialog pops up for this particular Private Key file. If none succeeded,
another Pass Phrase is queried on the terminal and remembered for the next
round (where it perhaps can be reused).

This scheme allows mod_ssl to be maximally flexible (because for N encrypted
Private Key files you can use N different Pass Phrases - but then
you have to enter all of them, of course) while minimizing the terminal
dialog (i.e. when you use a single Pass Phrase for all N Private Key files
this Pass Phrase is queried only once).

|/path/to/program [args...]

This mode allows an external program to be used which acts as a
pipe to a particular input device; the program is sent the standard
prompt text used for the builtin mode on
stdin, and is expected to write password strings on
stdout. If several passwords are needed (or an
incorrect password is entered), additional prompt text will be
written subsequent to the first password being returned, and more
passwords must then be written back.

exec:/path/to/program

Here an external program is configured which is called at startup for each
encrypted Private Key file. It is called with two arguments (the first is
of the form ``servername:portnumber'', the second is either
``RSA'', ``DSA'', or ``ECC''), which
indicate for which server and algorithm it has to print the corresponding
Pass Phrase to stdout. The intent is that this external
program first runs security checks to make sure that the system is not
compromised by an attacker, and only when these checks were passed
successfully it provides the Pass Phrase.

Both these security checks, and the way the Pass Phrase is determined, can
be as complex as you like. Mod_ssl just defines the interface: an
executable program which provides the Pass Phrase on stdout.
Nothing more or less! So, if you're really paranoid about security, here
is your interface. Anything else has to be left as an exercise to the
administrator, because local security requirements are so different.

The reuse-algorithm above is used here, too. In other words: The external
program is called only once per unique Pass Phrase.

This directive can be used to control the SSL protocol flavors mod_ssl should
use when establishing its server environment. Clients then can only connect
with one of the provided protocols.

The available (case-insensitive) protocols are:

SSLv2

This is the Secure Sockets Layer (SSL) protocol, version 2.0. It is the
original SSL protocol as designed by Netscape Corporation. Though its
use has been deprecated, because of weaknesses in the security of the protocol.

SSLv3

This is the Secure Sockets Layer (SSL) protocol, version 3.0, from
the Netscape Corporation.
It is the successor to SSLv2 and the predecessor to TLSv1. It's supported by
almost all popular browsers.

TLSv1

This is the Transport Layer Security (TLS) protocol, version 1.0.
It is the successor to SSLv3 and is defined in
RFC 2246.

This directive sets the all-in-one file where you can assemble the
Certificates of Certification Authorities (CA) whose remote servers you deal
with. These are used for Remote Server Authentication. Such a file is simply the
concatenation of the various PEM-encoded Certificate files, in order of
preference. This can be used alternatively and/or additionally to
SSLProxyCACertificatePath.

This directive sets the directory where you keep the Certificates of
Certification Authorities (CAs) whose remote servers you deal with. These are used to
verify the remote server certificate on Remote Server Authentication.

The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you can't just place the Certificate files
there: you also have to create symbolic links named
hash-value.N. And you should always make sure this directory
contains the appropriate symbolic links.

This directive sets the all-in-one file where you can
assemble the Certificate Revocation Lists (CRL) of Certification
Authorities (CA) whose remote servers you deal with. These are used
for Remote Server Authentication. Such a file is simply the concatenation of
the various PEM-encoded CRL files, in order of preference. This can be
used alternatively and/or additionally to SSLProxyCARevocationPath.

This directive sets the directory where you keep the Certificate Revocation
Lists (CRL) of Certification Authorities (CAs) whose remote servers you deal with.
These are used to revoke the remote server certificate on Remote Server Authentication.

The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you have not only to place the CRL files there.
Additionally you have to create symbolic links named
hash-value.rN. And you should always make sure this directory
contains the appropriate symbolic links.

This directive toggles the usage of the SSL/TLS Protocol Engine for proxy. This
is usually used inside a <VirtualHost> section to enable SSL/TLS for proxy
usage in a particular virtual host. By default the SSL/TLS Protocol Engine is
disabled for proxy both for the main server and all configured virtual hosts.

Note that the SSLProxyEngine directive should not, in
general, be included in a virtual host that will be acting as a
forward proxy (using <Proxy> or <ProxyRequest> directives.
SSLProxyEngine is not required to enable a forward proxy server to
proxy SSL/TLS requests.

This directive sets the all-in-one file where you keep the certificate chain
for all of the client certs in use. This directive will be needed if the
remote server presents a list of CA certificates that are not direct signers
of one of the configured client certificates.

This referenced file is simply the concatenation of the various PEM-encoded
certificate files. Upon startup, each client certificate configured will
be examined and a chain of trust will be constructed.

Security warning

If this directive is enabled, all of the certificates in the file will be
trusted as if they were also in
SSLProxyCACertificateFile.

This directive sets the all-in-one file where you keep the certificates and
keys used for authentication of the proxy server to remote servers.

This referenced file is simply the concatenation of the various PEM-encoded
certificate files, in order of preference. Use this directive alternatively
or additionally to SSLProxyMachineCertificatePath.

This directive sets the directory where you keep the certificates and
keys used for authentication of the proxy server to remote servers.

The files in this directory must be PEM-encoded and are accessed through
hash filenames. Additionally, you must create symbolic links named
hash-value.N. And you should always make sure this
directory contains the appropriate symbolic links.

This directive can be used to control the SSL protocol flavors mod_ssl should
use when establishing its server environment for proxy . It will only connect
to servers using one of the provided protocols.

When a proxy is configured to forward requests to a remote SSL
server, this directive can be used to configure certificate
verification of the remote server.

Note that even when certificate verification is enabled,
mod_ssl does not check whether the
commonName (hostname) attribute of the server certificate
matches the hostname used to connect to the server. In other words,
the proxy does not guarantee that the SSL connection to the backend
server is "secure" beyond the fact that the certificate is signed by
one of the CAs configured using the
SSLProxyCACertificatePath and/or
SSLProxyCACertificateFile directives.
In order to get this check done please have a look at
SSLProxyCheckPeerCN and
SSLProxyCheckPeerExpire directives which are off by
default.

The following levels are available for level:

none:
no remote server Certificate is required at all

optional:
the remote server may present a valid Certificate

require:
the remote server has to present a valid Certificate

optional_no_ca:
the remote server may present a valid Certificate
but it need not to be (successfully) verifiable.

In practice only levels none and
require are really interesting, because level
optional doesn't work with all servers and level
optional_no_ca is actually against the idea of
authentication (but can be used to establish SSL test pages, etc.)

This directive sets how deeply mod_ssl should verify before deciding that the
remote server does not have a valid certificate.

The depth actually is the maximum number of intermediate certificate issuers,
i.e. the number of CA certificates which are max allowed to be followed while
verifying the remote server certificate. A depth of 0 means that self-signed
remote server certificates are accepted only, the default depth of 1 means
the remote server certificate can be self-signed or has to be signed by a CA
which is directly known to the server (i.e. the CA's certificate is under
SSLProxyCACertificatePath), etc.

This configures one or more sources for seeding the Pseudo Random Number
Generator (PRNG) in OpenSSL at startup time (context is
startup) and/or just before a new SSL connection is established
(context is connect). This directive can only be used
in the global server context because the PRNG is a global facility.

The following source variants are available:

builtin

This is the always available builtin seeding source. Its usage
consumes minimum CPU cycles under runtime and hence can be always used
without drawbacks. The source used for seeding the PRNG contains of the
current time, the current process id and (when applicable) a randomly
chosen 1KB extract of the inter-process scoreboard structure of Apache.
The drawback is that this is not really a strong source and at startup
time (where the scoreboard is still not available) this source just
produces a few bytes of entropy. So you should always, at least for the
startup, use an additional seeding source.

file:/path/to/source

This variant uses an external file /path/to/source as the
source for seeding the PRNG. When bytes is specified, only the
first bytes number of bytes of the file form the entropy (and
bytes is given to /path/to/source as the first
argument). When bytes is not specified the whole file forms the
entropy (and 0 is given to /path/to/source as
the first argument). Use this especially at startup time, for instance
with an available /dev/random and/or
/dev/urandom devices (which usually exist on modern Unix
derivatives like FreeBSD and Linux).

But be careful: Usually /dev/random provides only as
much entropy data as it actually has, i.e. when you request 512 bytes of
entropy, but the device currently has only 100 bytes available two things
can happen: On some platforms you receive only the 100 bytes while on
other platforms the read blocks until enough bytes are available (which
can take a long time). Here using an existing /dev/urandom is
better, because it never blocks and actually gives the amount of requested
data. The drawback is just that the quality of the received data may not
be the best.

On some platforms like FreeBSD one can even control how the entropy is
actually generated, i.e. by which system interrupts. More details one can
find under rndcontrol(8) on those platforms. Alternatively, when
your system lacks such a random device, you can use a tool
like EGD
(Entropy Gathering Daemon) and run its client program with the
exec:/path/to/program/ variant (see below) or use
egd:/path/to/egd-socket (see below).

exec:/path/to/program

This variant uses an external executable
/path/to/program as the source for seeding the
PRNG. When bytes is specified, only the first
bytes number of bytes of its stdout contents
form the entropy. When bytes is not specified, the
entirety of the data produced on stdout form the
entropy. Use this only at startup time when you need a very strong
seeding with the help of an external program (for instance as in
the example above with the truerand utility you can
find in the mod_ssl distribution which is based on the AT&T
truerand library). Using this in the connection context
slows down the server too dramatically, of course. So usually you
should avoid using external programs in that context.

egd:/path/to/egd-socket (Unix only)

This variant uses the Unix domain socket of the
external Entropy Gathering Daemon (EGD) (see http://www.lothar.com/tech
/crypto/) to seed the PRNG. Use this if no random device exists
on your platform.

If an SSL renegotiation is required in per-location context, for
example, any use of SSLVerifyClient in a Directory or
Location block, then mod_ssl must buffer any HTTP
request body into memory until the new SSL handshake can be performed.
This directive can be used to set the amount of memory that will be
used for this buffer.

Note that in many configurations, the client sending the request body
will be untrusted so a denial of service attack by consumption of
memory must be considered when changing this configuration setting.

This directive specifies a general access requirement which has to be
fulfilled in order to allow access. It is a very powerful directive because the
requirement specification is an arbitrarily complex boolean expression
containing any number of access checks.

The implementation of SSLRequire is not thread safe.
Using SSLRequire inside .htaccess files
on a threaded MPM may cause random crashes.

The expression must match the following syntax (given as a BNF
grammar notation):

while for varname any variable from Table 3 can be used. Finally for
funcname the following functions are available:

file(filename)

This function takes one string argument and expands to the contents of the
file. This is especially useful for matching this contents against a
regular expression, etc.

Notice that expression is first parsed into an internal machine
representation and then evaluated in a second step. Actually, in Global and
Per-Server Class context expression is parsed at startup time and
at runtime only the machine representation is executed. For Per-Directory
context, specifically in a .htaccess context, this is different: here
expression has to be parsed and immediately executed for every request.

The OID() function expects to find zero or more instances
of the given OID in the client certificate, and compares the left-hand side
string against the value of matching OID attributes. Every matching OID is
checked, until a match is found.

This directive forbids access unless HTTP over SSL (i.e. HTTPS) is enabled for
the current connection. This is very handy inside the SSL-enabled virtual
host or directories for defending against configuration errors that expose
stuff that should be protected. When this directive is present all requests
are denied which are not using SSL.

This configures the storage type of the global/inter-process SSL Session
Cache. This cache is an optional facility which speeds up parallel request
processing. For requests to the same server process (via HTTP keep-alive),
OpenSSL already caches the SSL session information locally. But because modern
clients request inlined images and other data via parallel requests (usually
up to four parallel requests are common) those requests are served by
different pre-forked server processes. Here an inter-process cache
helps to avoid unnecessary session handshakes.

The following four storage types are currently supported:

none

This disables the global/inter-process Session Cache. This
will incur a noticeable speed penalty and may cause problems if
using certain browsers, particularly if client certificates are
enabled. This setting is not recommended.

nonenotnull

This disables any global/inter-process Session Cache. However
it does force OpenSSL to send a non-null session ID to
accommodate buggy clients that require one.

dbm:/path/to/datafile

This makes use of a DBM hashfile on the local disk to
synchronize the local OpenSSL memory caches of the server
processes. This session cache may suffer reliability issues under
high load.

shm:/path/to/datafile[(size)]

This makes use of a high-performance cyclic buffer
(approx. size bytes in size) inside a shared memory
segment in RAM (established via /path/to/datafile) to
synchronize the local OpenSSL memory caches of the server
processes. This is the recommended session cache.

dc:UNIX:/path/to/socket

This makes use of the distcache distributed session
caching libraries. The argument should specify the location of
the server or proxy to be used using the distcache address syntax;
for example, UNIX:/path/to/socket specifies a UNIX
domain socket (typically a local dc_client proxy);
IP:server.example.com:9001 specifies an IP
address.

Applies also to RFC 5077 TLS session resumption in Apache 2.2.28 and later

This directive sets the timeout in seconds for the information stored in the
global/inter-process SSL Session Cache, the OpenSSL internal memory cache and
for sessions resumed by TLS session resumption (RFC 5077).
It can be set as low as 15 for testing, but should be set to higher
values like 300 in real life.

Optionally configures a secret key for encrypting and decrypting
TLS session tickets, as defined in
RFC 5077.
Primarily suitable for clustered environments where TLS sessions information
should be shared between multiple nodes. For single-instance httpd setups,
it is recommended to not configure a ticket key file, but to
rely on (random) keys generated by mod_ssl at startup, instead.

The ticket key file must contain 48 bytes of random data,
preferrably created from a high-entropy source. On a Unix-based system,
a ticket key file can be created as follows:

dd if=/dev/random of=/path/to/file.tkey bs=1 count=48

Ticket keys should be rotated (replaced) on a frequent basis,
as this is the only way to invalidate an existing session ticket -
OpenSSL currently doesn't allow to specify a limit for ticket lifetimes.
A new ticket key only gets used after restarting the web server.
All existing session tickets become invalid after a restart.

The ticket key file contains sensitive keying material and should
be protected with file permissions similar to those used for
SSLCertificateKeyFile.

This directive sets whether a non SNI client is allowed to access a name based
virtual host. If set to on in the non default name based virtual
host, non SNI clients are not allowed to access this particular virtual host.
If set to on in the default name based virtual host, non SNI
clients are not allowed to access any name based virtual host belonging to
this IP / port combination.

This option is only available if httpd was compiled against an SNI capable
version of OpenSSL.

This directive sets the "user" field in the Apache request object.
This is used by lower modules to identify the user with a character
string. In particular, this may cause the environment variable
REMOTE_USER to be set. The varname can be
any of the SSL environment variables.

Note that this directive has no effect if the
FakeBasicAuth option is used (see SSLOptions).

This directive sets the Certificate verification level for the Client
Authentication. Notice that this directive can be used both in per-server and
per-directory context. In per-server context it applies to the client
authentication process used in the standard SSL handshake when a connection is
established. In per-directory context it forces a SSL renegotiation with the
reconfigured client verification level after the HTTP request was read but
before the HTTP response is sent.

The following levels are available for level:

none:
no client Certificate is required at all

optional:
the client may present a valid Certificate

require:
the client has to present a valid Certificate

optional_no_ca:
the client may present a valid Certificate
but it need not to be (successfully) verifiable.

In practice only levels none and
require are really interesting, because level
optional doesn't work with all browsers and level
optional_no_ca is actually against the idea of
authentication (but can be used to establish SSL test pages, etc.)

This directive sets how deeply mod_ssl should verify before deciding that the
clients don't have a valid certificate. Notice that this directive can be
used both in per-server and per-directory context. In per-server context it
applies to the client authentication process used in the standard SSL
handshake when a connection is established. In per-directory context it forces
a SSL renegotiation with the reconfigured client verification depth after the
HTTP request was read but before the HTTP response is sent.

The depth actually is the maximum number of intermediate certificate issuers,
i.e. the number of CA certificates which are max allowed to be followed while
verifying the client certificate. A depth of 0 means that self-signed client
certificates are accepted only, the default depth of 1 means the client
certificate can be self-signed or has to be signed by a CA which is directly
known to the server (i.e. the CA's certificate is under
SSLCACertificatePath), etc.

Example

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